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Water and slope

Microcatchment (Negarim)

Terra Humana editorial teamLast updated: 2026-10-127 min read

A young tree with straw mulch in a small microcatchment whose earth ridges lead rainwater to it; a little water stands at the lowest point

In brief

A small earth-bunded area that guides rainwater running off its surface to the foot of a single tree, so one plant receives the rain of a much larger patch.

What is a microcatchment?

A microcatchment is a small piece of ground shaped so that the rain falling on it does not run away but flows to one point, where a tree or shrub stands. Low bunds of earth mark the edges, the surface inside slopes slightly towards a basin, and the plant in that basin drinks not only the rain falling on its own spot but the runoff of a patch several times larger. The ratio between the collecting area and the planted area is the heart of the method: the drier the site, the larger the share that has to feed each plant.

The best-known form is the Negarim microcatchment: rows of diamond-shaped basins, each framed by small bunds, with an infiltration pit in the lowest corner. The FAO water harvesting manual by Will Critchley and Klaus Siegert describes it as suitable for trees where annual rainfall can be as low as 150 millimetres, on slopes of up to about five percent and on soils at least one and a half metres deep. A single unit usually covers between 10 and 100 square metres, depending on the species. The name comes from the Hebrew word for runoff. It points to the Negev Desert, where Michael Evenari, Leslie Shanan and Naphtali Tadmor rebuilt and studied ancient runoff farms from the 1950s onwards and showed that crops and trees can grow on rain that seems far too little.

In German usage the everyday form is the Gießmulde: the ring of earth around a freshly planted tree that keeps rain and watering water in place. It is the same principle at the smallest scale.

One tree drinks the rain,of a larger patchLearning panel on the microcatchment: a tree drinks not only the rain falling on its own spot but the runoff of a patch several times larger. The drier the site, the more area each tree needs. The Negarim from above: diamond-shaped basins framed by small bunds, the water flows downhill to a pit in the lowest corner, where the tree stands. Guide values for trees from the FAO manual: 10 to 100 square metres per unit, bunds 25 centimetres high or more, slope up to about 5 percent, soil depth of 1.5 metres or more. In section: the bund slows the running water, in the basin it soaks in deeply, mulch protects against evaporation. In the Mediterranean, winter rain fills the soil below the tree, and in the first summer the roots draw on that store. What comes with it: check the bunds after every significant rain, do not dig too deep on heavy soil so the roots do not stand in water, and remember that a microcatchment creates no new water; the catchment area itself stays drier. TERRAWIKI · LEARNING PANEL One tree drinks the rainof a larger patch The drier the site, the more area per tree. 1THE NEGARIM FROM ABOVE catchment area bund pitwith tree downhill10 to 100 m²per unit25 cm or morebund heightup to about 5%slope1.5 m or moresoil depth Guide values for trees from the FAO manual 2IN SECTION: SLOW, SOAK, PROTECT bund mulch catchment area winter store in the soil 1231The bund slows the running water.2In the basin it soaks in deeply.3Mulch protects against evaporation. In the Mediterranean, winter rain fills the soil below thetree. In the first summer the roots draw on that store. 3WHAT COMES WITH IT Tend the bunds check afterevery significantrain Not too deep on heavy soil theroots would standin water No new water the catchmentarea itself staysdrier Basis: Critchley and Siegert, FAO (1991) · TerraWiki: Microcatchment

A family of shapes

Microcatchments are one branch of rainwater harvesting, the branch that works plant by plant instead of slope by slope. Their relatives differ mainly in shape and size. The half-moon, a semicircular bund open towards the slope, comes from the Sahel and catches water for a planting zone inside its arc. The zaï pit, also from West Africa, is the smallest of them: a hand-dug hole with compost or manure at the bottom, which concentrates water and nutrients for a single plant. At the other end of the scale stand swales, terraces and keyline design, which spread water along whole contour lines.

What they share is a sequence: slow the water, let it sink in, protect it from evaporation. The last step is often forgotten. A basin of bare soil in the sun loses much of what it has caught. A layer of mulch, leaves or cuttings in the basin keeps the soil cool and the water in it.

Microcatchments in the Mediterranean

In the Sahel the rain falls in summer, in the growing season, when plants need it most. In the Mediterranean, as in the Negev, it is the other way round: rain comes in autumn and winter, and the summer is dry. That shifts the purpose of a microcatchment. Its task here is to fill the soil profile below the tree as deeply as possible during winter, so that the roots can draw on that store in the first and second summer. A tree whose roots follow the moisture downwards gains a head start that no watering can of the following July can give it.

The method has a Mediterranean history of its own. Spanish forestry researchers around Andrés Martínez de Azagra at the University of Valladolid have worked since the late 1990s on what they call oasification: shaping the ground during afforestation of dry slopes in Spain so that small basins collect runoff, soil and nutrients for each seedling, and calculating how large each catchment must be. In Tunisia, olive groves have long been fed by runoff from uncultivated upper slopes.

How Terra Humana understands it

For Terra Humana the microcatchment is the most direct answer to the hardest moment in the life of a planted tree: its first dry summer. It needs no machine, can be built with a spade and adjusted every year, and every tree can receive one shaped to its spot. That makes it a tool of patience and attention rather than of large earthworks.

The method also has limits that belong in any honest description. On heavy soils a deep basin can hold water for too long after a storm, so many practitioners, Brad Lancaster among them, place the plant slightly above the lowest point instead of in it. Bunds break in cloudbursts and must be repaired, which the FAO manual expressly stresses. And a microcatchment does not create water: it redistributes what falls. Where a tree takes the runoff of 20 square metres, those 20 square metres stay drier. On a slope where water is to stay in the land, microcatchments are therefore one piece in a larger pattern together with ground cover, swales and the protection of the soil against desertification.

The valley of Sa Medada near Jerzu, Sardinia, with olive grove and macchia

Sa Medada

What this looks like at Sa Medada

Sa Medada lies on the eastern side of Sardinia, and the dry season runs from May to September. For a young tree the first summer is the hardest test. The first tree planted on the land, a service tree in 2024, stands on a very hot southern flank. Project Eden begins with pioneer plants, ground cover and holding water; the watering basin around a single tree is the smallest form of that last step.

More about Project Eden

Frequently asked

What is a microcatchment?

A microcatchment is a small, deliberately shaped piece of ground that collects the rain falling on it and sends it to one planting point. Low earth bunds mark its edges, and the surface inside slopes gently towards a basin where a tree or shrub stands. The idea is a simple multiplication: the plant does not live on the rain that falls on its own small footprint, but on the runoff of an area several times larger. That is why microcatchments work even where the annual rainfall alone would not keep a young tree alive.

What does Negarim mean?

Negarim is the name of a particular microcatchment form: diamond-shaped basins framed by small bunds, with an infiltration pit in the lowest corner where the tree is planted. According to the FAO water harvesting manual by Critchley and Siegert, the word goes back to the Hebrew term for runoff. The form was developed in the Negev Desert in Israel, where researchers around Michael Evenari studied ancient runoff farms, although the manual notes that the first reports of the technique come from southern Tunisia.

How big should a microcatchment be?

There is no single right size, because it depends on rainfall, soil and the plant. The FAO manual gives a range of roughly 10 to 100 square metres per unit for trees, with bunds at least 25 centimetres high, on slopes of up to about five percent and on soils that are at least one and a half metres deep. Drier sites need a larger catchment per tree, wetter ones a smaller one. On heavy soils the basin should not be dug too deep, so that the roots do not stand in water after a storm.

Is a microcatchment the same as a watering basin around a tree?

It is the same family. The ring of earth that gardeners pile up around a freshly planted tree is the smallest and simplest microcatchment: it stops irrigation water and rain from running away. A designed microcatchment goes one step further and enlarges the surface that drains to the tree, so that it harvests rain from beyond the tree's own footprint. Half-moons and zaï pits are related forms from the Sahel, while swales and terraces carry the same principle to the scale of a whole slope.

Do microcatchments need maintenance?

Yes, especially in the first years. A heavy storm can break a bund, and an unrepaired breach lets water out and tends to widen with each following rain. The FAO manual therefore advises inspecting the bunds after every significant rainfall and repairing damage at once. A layer of mulch in the basin keeps the collected water from evaporating, and grass or low vegetation on the bunds protects them from washing away. Once the tree has rooted deeply, the structure matters less and can slowly level out.

Seen from above: only the rim and clay lid of a buried olla show at ground level in a straw-mulched bed, a ring of bare dark soil around it, tomatoes, basil and peppers close byNext in this themeOlla IrrigationIrrigation with an unglazed clay pot buried up to its neck and filled with water, which seeps slowly through the porous wall into the soil around the roots.

Related terms

Two swales along the contour after rain: still water in the level trenches, mulched berms with plants belowRainwater Harvesting & SwalesHolding rain where it falls: soaking it into ditches and basins, storing it in dams and cisterns, spreading it along the shape of the slope.Aerial view of almost level dry rangeland with many half-moons in staggered rows, each with some green insideHalf-Moon (Demi-lune)A semicircular earth bund opening uphill, which catches runoff in its arc and lets it soak into a planting zone; a Sahel method of water harvesting.Rows of small planting pits with compost and young seedlings in hard, crusted soilZaï PitA small planting pit dug into hard, crusted soil and filled with manure or compost, which gathers rain and nutrients for one plant; from West Africa.Aerial view of a slope with planting rows along the contoursKeyline DesignA land-planning method that reads a slope's shape to move rainwater from moist valleys toward drier ridges, storing it in the soil.A lifted layer of straw and wood-chip mulch with moist dark soil underneath, next to a dry, cracked pathMulchA layer of organic or mineral material on the soil surface that cuts evaporation, keeps the ground cooler, stops erosion and feeds soil life.Erosion gullies on a bare slope after heavy rain, with muddy runoffSoil ErosionThe removal of soil by water or wind. Bare ground and steep slopes multiply it, and what is lost in an hour takes centuries to form again.

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Sources

  • Critchley, W. and Siegert, K., Water Harvesting: A Manual for the Design and Construction of Water Harvesting Schemes for Plant Production, FAO (1991)
  • Evenari, M., Shanan, L. and Tadmor, N., The Negev: The Challenge of a Desert, 2nd edition, Harvard University Press (1982)
  • Lancaster, B., Rainwater Harvesting for Drylands and Beyond, Vol. 1, 3rd edition (2019) and Vol. 2, 2nd edition (2019), Rainsource Press
  • Martínez de Azagra Paredes, A., Mongil Manso, J., del Río, J. and Rojo Serrano, L., Conceptos, modelos y ejemplos sobre oasificación, Ecología 20 (2006) 453 to 470

Last updated: 2026-10-12